The proposed work will provide an empirical basis for relating the thermoregulatory responses produced by preoptic/anterior (PO/AH) chemical stimulation in behaving animals to the underlying neuronal mechanisms mediating those regulatory responses. These experiments are designed to examine directly the effect of biogenic hypothalamic compounds, notably acetylcholine (ACh), 5-hydroxytryptamine (5-HT), and norepinephrine (NE), on the activity of thermoregulatory neurons in rats and ground squirrels. Observations on the responsiveness of cells classified as thermodetectors and thermosensitive interneurons to biogenic compounds and the flow of electrical current are intended to clarify functional differences between these two proposed types of neurons. Experiments on ground squirrels (Citellus lateralis) are intended to investigate the properties of PO/AH thermoregulatory neurons in hibernators during their active (non-hibernating) period.